SwiftUI 学习笔记 61: Swift基础复习（一）

var f: Character = "A"

type(of: a)

//单行注释

/*
多行注释
多行注释
*/

var a: Int? = 2

print(Int("123123")) -> Optional(123123)
print(Int("123123") ?? 10) -> 123123
print(Int("hello") ?? 10) -> 10
print(Int("12")!) -> 12

var a: Int? = 2

if a == nil {
    print("a没有值")
}else{
    print("a的值为：\(a!)")
    
    print("a的值为：" + String(a!))
}

var a = ("hello", 12, false, 12.5)
var b: (String, Int) = ("hi", 12)
b.1 = 99

print(a.0)
print(b.1)

/*
hello
99
*/

//我们可以给元组起名
var c = (name1: "hi", name2: 1212)

print(c)
print(c.name1)
print(c.0)

//也可以在声明时取名
var d: (name1: String, name2: Int) = ("hello", 12)

print(d.name1)

//我们利用元组直接创建变量或常量
let (name1, name2) = ("Hello", 12)

print(name1)

//也可以使用下划线忽略
let (name1, _, name2) = ("Hello", true, 12)

print(name1, name2)

let hello: Int? = 12

if let txt = hello {
    print(txt)
}
/*
else{

}
*/

let a: Int![]= 12
let b: Int = a

print(b)

//或者写成
let c: Int? = 14
let d = c!

print(d)

let num = 11

switch num {
case 11:
    print("情况1")
    fallthrough
case 12:
    print("情况2")
case 13:
    print("情况3")
default:
    print("没有匹配")
}

let num = (12, true)

switch num {
case let(name1, false):
    print(name1)
case let(12, name2):
    print(name2)
default:
    print("没有匹配")
}

/*
true
*/

let a = (10, 20)

switch a {
case let(name1, name2) where name1 > name2:
    print(name1 - name2)
case let(10, name2):
    print(10 + name2)
default:
    print("不符合要求")
}

/*
输出：
30
*/

//不包含结尾
for num in stride(from: 0, to: 10, by: 2){
    print(num)
}

/*
输出：
0
2
4
6
8
*/

//包含结尾
for num in stride(from: 0, through: 9, by: 3){
    print(num)
}

/*
输出：
0
3
6
9
*/

//反向
for num in stride(from: 0, through: 9, by: 3).reversed(){
    print(num)
}

/*
输出
9
6
3
0
*/

for num in 0...12 {
    if num == 3 {
        continue
    }
    if num == 5 {
        break
    }
    
    print(num)
}

/*
输出：
0
1
2
4
*/

var a = 0
var b = true

repeat {
    print(a)
    a += 1
    
    if a == 5 {
        b.toggle()
    }
}while b

/*
输出：
0
1
2
3
4
*/

import Cocoa
// 字符串长度
var str = "ABCDEF"
print(str.count)

/*
 6
 */

//字符串开头字符
print(str[str.startIndex]) //str.startIndex为开头

/*
 A
 */

//字符串结尾字符
print(str[str.index(before: str.endIndex)]) // str.endIndex指的是最后一个字母后面的值，所以用index的before来取最后一个字母
print(str[str.index(after: str.startIndex)]) // 取第二个字母

/*
 F
 B
 */

//根据索引取任意位置字符
print(str[str.index(str.startIndex, offsetBy: 3)]) //取索引为3的字符，索引从0开始

/*
 D
 */

//字符串区间
var a = str.index(str.startIndex, offsetBy: 2)
var b = str.index(str.startIndex, offsetBy: 5)

print(str[a...b])
print(str[a..<b])

/*
 CDEF
 CDE
 */

//获取某个字符第一次出现的索引
var c = str.firstIndex(of: "E") ?? str.endIndex //因为是可选值，字符串中不含E则返回nil，所以需要使用??
print(str[str.startIndex...c])

/*
 ABCDE
 */

//获取从索引0开始，长度为4的字符
print(str.prefix(4))

/*
 ABCD
 */

//获取后两位字符
print(str[str.index(str.endIndex, offsetBy: -2)..<str.endIndex])

/*
 EF
 */

//查找字符串是否包含某字符
print(str.contains("CD"))
print(str.contains("G"))

/*
 true
 false
 */

//查找字符串中是否包含某个字符串中的某个字符
print(str.contains(where: String.contains("AKK")))
print(str.contains(where: String.contains("KKK")))

/*
true
false
*/

//判断前缀是否为字符串
print(str.hasPrefix("ABC"))
print(str.hasSuffix("EF"))

/*
 true
 true
 */

//追加字符串
str.append("sssssssss")
print(str)

/*
 ABCDEFsssssssss
 */

str = String(str.prefix(6)) //str = "ABCDEF"

//插入字符串
str.insert(contentsOf: "OPQ", at: str.index(str.startIndex, offsetBy: 4))
print(str)

/*
 ABCDOPQEF
 */

//根据索引修改字符串
str = "ABCDEF" //初始化
let d = str.firstIndex(of: "B") ?? str.startIndex
let e = str.firstIndex(of: "E") ?? str.index(before: str.endIndex)

str.replaceSubrange(d...e, with: "123123")

print(str)

/*
 ABCD123123EF
 */

//根据字符串替换字符串
str = "ABCDEF" //初始化
str.replacingOccurrences(of: "ABC", with: "888")
print(str)

/*
 ABCDEF
 */

//根据索引删除字符
str = "ABCDEF" //初始化
str.remove(at: str.index(str.startIndex, offsetBy: 2))
print(str)

/*
 ABDEF
 */

//根据范围删除字符
str = "ABCDEF" //初始化
str.removeSubrange(str.index(str.startIndex, offsetBy: 1)...str.index(str.startIndex, offsetBy: 3))
print(str)

/*
 AEF
 */

//直接遍历字符串
str = "ABCDEF" //初始化
for item in str {
    print(item)
}

/*
 A
 B
 C
 D
 E
 F
 */

//用索引遍历字符串
for item in 0..<str.count {
    print(str[str.index(str.startIndex, offsetBy: item)])
}

/*
 A
 B
 C
 D
 E
 F
 */

//多行文本
var mtxt = """
            hello
                        world
"""

print(mtxt)

/*
 hello
             world
 */

//无视转译符号输出字符串
var utxt = #""hello\ntxt"#
print(utxt)

/*
"hello\ntxt
 */